The instant invention relates generally to eddy current proximity probe systems for determining displacement motion and position of an observed conductive target object and in particular, to a multi-coil eddy current proximity probe system utilized for monitoring, for example, rotating and reciprocating machinery.
Proximity probe systems that analyze and monitor, for example, rotating and reciprocating machinery are known in the art. These systems typically include one or more proximity probes: noncontacting eddy current displacement devices operating on the eddy current principle for measuring displacement motion and position of an observed conductive target object relative to one or more of the displacement devices. Typically, each proximity probe is located proximate a target object such as a rotating shaft of a machine or an outer race of a rolling element bearing being monitored and is connected to signal conditioning circuitry which in turn is coupled to analyzing apparatus for data reduction and display. By known techniques, these systems analyze and monitor rotating and reciprocating machinery for providing, inter alia, indications of incipient problems. A variety of proximity probes and systems are at the present time being sold by the assignee of this application, Bently Nevada Corporation of Minden, Nev.
Generally, a proximity probe system includes a proximity probe comprised of a multi-conductor probe cable coupled to an inductor or coil that is situated at a forward most end of the probe. The coil is coupled to the signal conditioning circuitry of the system via the probe cable and is driven by a radio frequency signal from the signal conditioning circuitry and in turn creates an alternating magnetic field in any proximate conductive target object. This magnetic field produces eddy currents in the object that induce a counter electromotive force (emf) in the coil that alters the impedance of the probe and thus the output of the probe as a function of distance between the probe and observed target object. The signal conditioning circuitry demodulates the probe output and provides output signals proportional to a distance or gap interposed between the proximity probe and the observed conductive target object. Thus, the signal conditioning circuitry is also sometimes referred to as an oscillator-demodulator device.
The above-delineated system is burdened by temperature errors due to temperature variations in the multi-conductor cables, the coil and the electronics associated with the signal conditioning circuitry. Additionally, temperature variations in the targets themselves cause temperature stability problems within the system. Furthermore, component and manufacturing variations also generally burden the system.
Moreover, and more particularly, sense coil resistance of the probe is one principle source of temperature drift error. Thus, the process of measuring gap as a function of the impedance of the coil is susceptible to this error thereby resulting in inaccurate proximity probe measurements as a consequence of the drift error causing a false appearance of a gap change between the target and probe. Such inconsistencies in temperature stability of the proximity probe result in unpredictable and unreliable measurements even when the proximity probe is functioning in its linear range of operation.
U.S. Pat. No. 5,854,553 to Barclay, et al. teaches the use of a digitally linearizing eddy current probe wherein the output of an eddy current probe is demodulated and subsequently linearized using an analog to digital converter, a digital signal processor, and a memory. The linearized digital output signal is converted back to an analog signal, the voltage of which is used as being directly proportional to the position of the conductive target in relation to the probe. Hence, the U.S. Pat. No. 5,854,553 to Barclay, et al. measures the gap, as a function of the impedance of the coil being driven to engender or set up eddy currents in the target object. Thus, U.S. Pat. No. 5,854,553 to Barclay, et al. also suffers from, inter alia, the same temperature instability problems delineated hereinabove.
Moreover, known multiple coil proximity switch devices, distance measurement devices, and metal detecting circuits are also plagued by, inter alia, temperature drift error and component and manufacturing variations.
For the foregoing reasons, it would be highly desirable to provide an eddy current proximity probe system that would be accurate, reliable, and substantially unaffected by temperature, component and manufacturing variations. More specifically, it would be highly desirable to provide a proximity probe system that compensates for different probe cable lengths, resistance changes in the cable and the probe coil, and temperature changes in the probe cable, coil, and signal conditioning devices.
The instant invention is distinguished over the known prior art in a multiplicity of ways. For one thing, the instant invention provides a multi-coil eddy current proximity probe system that provides accurate and reliable measurements over a wide range of circuit and environmental conditions. Particularly, the instant invention provides an eddy current proximity probe system that includes a unique multi-coil proximity probe and processing and control circuitry that generally eliminates temperature errors and manufacturing and component variations. For example, the unique multi-coil probe, and processing and control circuitry provides a stable output with different probe cable lengths, with resistance changes in the cables and probe coils, and with temperature changes in the probe cables, coils, and circuitry thereby providing accurate and reliable measurements of machine operating characteristics. Furthermore, the eddy current proximity probe system generally solves the problem of compensating for changes in the conductivity, permeability, and temperature profiles of different target materials. Moreover, and in stark contrast to the known prior art, the instant invention detects a current in a sense coil separate from a coil driven to engender or set up eddy currents in a target object for determining gap values.
In one form of the instant invention, the eddy current proximity system includes a multi-coil proximity probe including a sense coil, a drive coil, and a reference coil. The coils are located adjacent one another with their interiors or hollow cores coaxially arranged along a common longitudinal axis. The drive coil is interposed between the sense coil and the reference coil such that the sense coil is positioned at a forwardmost end of the probe. The system is further comprised of a signal conditioning and control system having a feed back loop comprised of a first phase detector or first multiplier circuit and a signal generator having an automatic gain controller. The first multiplier includes an input coupled to the reference coil via a multi- conductor cable and an output electrically connected to the automatic gain controller. An output of the automatic gain controller is coupled to the signal generator that is coupled to the drive coil via a multi-conductor cable. The signal generator drives the drive coil with an alternating drive signal that generates a first magnetic field that radiates from the drive coil and induces an alternating reference signal in the reference coil. Any phase discrepancy in the reference signal results in a control signal being sent from the multiplier to automatic gain controller which provides a corrective control signal which automatically adjusts the gain of the signal generator for controlling the amplitude of the drive signal. Thus, the input signal driving the drive coil is a function of its own magnetic field output. Additionally, any attenuation by the cable coupling the reference coil to the first multiplier is corrected for by the closed feedback loop between the drive coil and the reference coil. Furthermore, temperature variations, manufacturing variations and component variations are inside the closed feedback loop and are thus compensated.
The first magnetic field radiating from the drive coil also induces eddy currents in any proximate conductive target object. Thus, when the forwardmost end of probe is positioned adjacent a conductive target object the eddy currents induced therein in turn emanate a second magnetic field. The sense coil that is interposed between the drive coil and the conductive target object senses this second magnetic field. As a result, an alternating sense signal is induced in the sense coil that has a signature that is a function of the distance or gap between the probe and the conductive target object. A multi-conductor cable, preferably of the same length as the cable coupling the reference coil to the first phase detector, transmits the sense signal to a processor/analyzer system where it is conditioned into signals proportional to the distance or gap between the probe and the conductive target object.
It is important to note that the second magnetic field created by the first magnetic field is substantially a function of spacing as a result of the instant invention holding the first magnetic field substantially constant while the signal driving the drive coil may be fluctuating as a result of temperature, component and manufacturing variations.
Accordingly, a primary object of the instant invention is to provide a new, novel and useful multi-coil eddy current proximity probe system: apparatus and method.
A further object of the instant invention is to provide a system as characterized above that includes a multi-coil eddy current proximity probe and a signal conditioning and control system.
Another further object of the instant invention as characterized above is to provide a closed loop feedback and control system for feeding back a signal from a reference coil to a drive coil for controlling the signal driving the drive coil and thus its radiated magnetic field.
Another further object of the instant invention is to provide a signal conditioning and control system as characterized above which includes a closed loop feedback and control system comprised of a drive coil carrying an alternating current for emanating a first magnetic field for inducing eddy currents in a target object and a feed back loop for controlling the first magnetic field, the system further includes a sense coil interposed between the target object and drive coil for sensing, during the control of the first magnetic field, an induced alternating current correlative to the gap between the probe and target object.
Another further object of the instant invention is to provide the multi-coil eddy current proximity probe system as characterized above which eliminates temperature errors, and manufacturing and component variations as a consequence of the instant invention including them in a closed loop feedback and control system which extends all the way out to a tip of the probe.
Another further object of the instant invention is to provide the multi-coil eddy current proximity probe system as characterized above which senses current that fluctuates in value as the target object to probe distant fluctuates.
Another further object of the instant invention is to provide the multi-coil eddy current proximity probe system as characterized above which opposes changes of an output of a radiated magnetic field from a drive coil (an output increase or an out put decrease) while measuring a current in a sense coil correlative a target object and sense coil proximity.
Another further object of the instant invention is to provide the multi-coil eddy current proximity probe system as characterized above which positions the reference coil to be inductively coupled to the drive coil and substantially uninfluenced by the eddy current induced magnetic field.
Viewed from a first vantage point, it is an object of the instant invention to provide a multi-coil eddy current proximity probe system, comprising in combination: a drive coil located proximate a conductive target object and radiating a first magnetic field by carrying an alternating current for inducing eddy current within said conductive target object and causing a second magnetic field to be radiated from said conductive target object; a control means operatively coupled to said drive coil for controlling said alternating current carried by said drive coil as a function of its own radiated said first magnetic field; a sense coil interposed between said drive coil and said conductive target object for sensing, during the control of said first magnetic field radiating from said drive coil, said second magnetic field radiating from said conductive target object such that an alternating current correlative to a position between said sense coil and said conductive target object is induced within said sense coil, and a processor operatively coupled to said sense coil for processing said induced alternating current in said sense coil and transforming said induced alternating current into output signals correlative to said position between said sense coil and said conductive target object.
Viewed from a second vantage point, it is an object of the instant invention to provide a multi-coil eddy current proximity probe system, comprising in combination: three coaxially disposed coils including a sense coil, a drive coil and a reference coil; said drive coil interposed between said sense coil and said reference coil and operatively coupled to and coating with a controllable current source for carrying a controlled alternating current delivered from said controllable current source and for radiating a first magnetic field from said drive coil to an adjacent conductive target object for generating eddy currents within said conductive target object resulting in a second magnetic field radiating from said conductive target object; said reference coil inductively coupled to said drive coil by said first magnetic field such that a first current indicative of said first magnetic field is induced within said reference coil; control means including a feedback loop means comprised of said reference coil and said controllable current source for processing said induced first current indicative of said first magnetic field and controlling said controllable current source as a function of said induced first current indicative of said first magnetic field for delivering said controlled alternating current to said drive coil such that said controlled alternating current delivered to said drive coil controls said first magnetic field radiated from said drive coil; said sense coil inductively coupled to said adjacent target object for sensing said second magnetic field radiating from said conductive target object such that a second current correlative to a position between said sense coil and said conductive target object is induced within said sense coil during said control by said control means of said first magnetic field radiating from said drive coil, and a processor operatively coupled to said sense coil for processing said induced second current in said sense coil and transforming said induced second current into output signals correlative to said position between said sense coil and said conductive target object.
Viewed from a third vantage point, it is an object of the instant invention to provide a multi-coil eddy current proximity probe system, comprising in combination: a first coil; a signal generator operatively coupled to said first coil; said first coil emanating a first magnetic field by carrying a first alternating current delivered from said signal generator to said first coil, said first magnetic field inducing eddy currents within an adjacent conductive target object causing a second magnetic field to emanate back toward said first coil; a second coil inductively coupled to the adjacent conductive target object and interposed between said first coil and the adjacent conductive target object; said second coil carrying a second alternating current induced by said second magnetic field and correlative to a position of the adjacent conductive target object; a third coil located adjacent said first coil and carrying a third alternating current induced by said first magnetic field emanating from said first coil; means for controlling said first alternating current carried in said first coil as a function of the said third alternating current induced by said first magnetic field radiating from said first coil for substantially holding said first alternating current carried in said first coil substantially constant, and means for receiving said second alternating current and transforming said received second alternating current into output signals correlative to the position of the adjacent conductive target object while holding said first alternating current carried in said first coil substantially constant for monitoring the position of the conductive target object.
Viewed from a fourth vantage point, it is an object of the instant invention to provide a method for determining a position of a conductive target object of a machine for monitoring the machine for indications of incipient problems, the steps including: locating a drive coil proximate the conductive target object; interposing a sensing coil between the drive coil and the conductive target object; driving the drive coil with an alternating signal for generating eddy currents in the conductive target object; detecting a signal in the sensing coil induced by a magnetic field radiating from the conductive target object produced from the eddy currents in the target object, and transforming said signal into a output signal correlative to the position of the conductive target object, and determining if said output signal is an indication of an incipient machine problem.
These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.